X-ray security inspection machines are widely used at security checkpoints, such as those in airports, malls, courthouses, government offices, embassies, schools, and prisons. Where space is not restricted or where an X-ray security inspection machine is required on a permanent basis, the machine may be set up and configured on site, and retained there indefinitely. Such machines are provided in various sizes and specifications, depending on their intended application.
Nevertheless, as the issue of security becomes an ever greater priority, there is an increasing demand for X-ray security inspection machines which find more widespread application. In particular, there is a need for X-ray security inspection machines which may be employed in space-restricted environments and/or which are readily moveable, i.e. portable, from one location to another. Most of the currently available machines are heavy, bulky, and not readily portable. Additionally, most of the currently available security screening systems cannot be easily and efficiently deployed in outdoor environments or at temporary venues, where they are frequently needed to scan for threats inside small baggage items such as backpacks and purses. Typically, tedious and sometimes ineffective hand-searches of small items must be performed.
In most X-ray systems, a highly collimated continuous wave (CW) X-ray source is used, which covers the objects being scanned with a thin fan beam. This has an advantage that a relatively inexpensive linear array of dual-energy detectors can be used for generating the image, while providing the capability of organic/inorganic discrimination based on a thin front detector to detect lower-energy X-rays and a thicker rear detector to detect higher-energy X-rays. The ratio of low-to-high-energy X-ray signal is used for material discrimination. However, a limitation of this approach is that most of the X-rays emitted by the source are absorbed in the collimator, and the X-ray source has to be on continuously to cover the full extent of the object. This leads to a required large amount of shielding in all directions except for the forward fan beam, and also power consumption is high. Such systems therefore tend to be heavy and/or bulky, making them difficult to transport from one place to another.
Dual-energy imaging is typically used to image bags and parcels in the security industry. In X-ray baggage scanners, however, a line array of dual-layer detectors is used. The detector layer closest to an X-ray source is used to primarily detect low-energy X-rays and the detector layer furthest from the source, usually filtered by some filtration material such as copper, is used to primarily detect high-energy X-rays. A width of the detector is typically on the order of 1 mm, and a continuous X-ray source is required to scan objects 1 mm or so, at a time. With an intense X-ray source that is collimated to a fan beam, objects can be scanned at speeds of the order of 20 cm/s. All other X-rays emitted by the source need to be stopped by shielding.
There is a need, therefore, for an improved X-ray security inspection system that may be employed in space-restricted environments and/or which is readily moveable, i.e. portable, from one location to another. Also, there is a need for a security inspection system that is compact, light-weight, and can be ported to temporary and/or outdoor venues.